The invention relates to a device for monitoring the supply of printing fluid in a reservoir for an ink printing device which changes its supply volume in accordance with consumption of the printing fluid.
In typical ink printing devices, a printing head is moved by a drive means along a recording medium and is supplied with printing ink by a supply system from a storage reservoir. The printing head may be a mosaic printing head having several piezoelectrically operated nozzles. Because of the contraction processes which take place in these nozzles during the printing operation, a printing head of this type is supplied automatically with printing fluid. If the ink reservoir is made an integral part of the printer head, as has been proposed, then simple visual monitoring of the ink supply in a reservoir is not readily possible. However, continuous monitoring of the ink supply is essential when printers of this kind are used in teleprinter and dataprinter applications.
One device for determining the ink level in a printer head ink reservoir is disclosed in the British Specification No. 1574527. There, two electrodes are disposed in the base of the ink reservoir for wetting by printing fluid when present in the reservoir. An electrical circuit is connected to the electrodes and arranged to detect the electrical resistance therebetween and to provide a signal at a predetermined value of the resistance. A display device responsive to the signal provides a warning indication when the ink reservoir is essentially empty of printing fluid. If an ink reservoir is to be manufactured economically as a simple throwaway product, then the manufacture of ink reservoirs with electrodes integrated into their bases substantially raises the product costs. In addition, this type of ink monitoring arrangement requires additional electrical connections which must be arranged on the printing carriage.
British Specification No. 1554481 discloses an ink storage container which is economical and readily replaceable in the ink printing device. The storage container utilizes a weighted cover component disposed over the ink supply for producing a temporary increased pressure in the container. The brief increases in ink pressure are necessary for ink printing devices utilizing piezoelectrically driven printing nozzles in order to eliminate air trapped in the supply system, which may be caused when the ink printing device is placed in operation or when the ink reservoir container is interchanged.
The present invention provides for a simple and economical device for monitoring fluid supply in an ink reservoir container for use with an ink printing device having an interchangeable ink reservoir container integrated into a printing head having piezoelectrically operated nozzles.